A filter device is commonly disposed in the exhaust passage of an engine. The filter device is operative to collect particulate matter exhausted from the engine to thereby inhibit release of the particulate matter into the atmosphere. A PM sensor is disposed downstream from the filter device. This enables determination of whether there is a malfunction, such as a cracking failure or a melting loss, in the filter device to be carried out.
For example, a filter malfunction determination apparatus disclosed in patent literature 1 includes a pair of opposite electrodes installed to a PM sensor disposed downstream of a filter device. The filter malfunction determination apparatus uses a reduction in the resistance across the opposite electrodes due to the amount of deposited particulate matter between the opposite electrodes.
Specifically, the filter malfunction determination apparatus is adapted to determine that there is a malfunction in the filter device upon determination that the amount of the deposited particulate matter between the opposite electrodes during a predetermined malfunction determination period is equal to or more than a predetermined amount.